Field of the Invention
The present invention concerns the determination, in particular the quantitative determination, of various parameters in a volume section by the operation of a magnetic resonance apparatus.
Description of the Prior Art
For the purpose of determining specific parameters of a volume section by the operation of a magnetic resonance apparatus, also referred to as quantitative MR, use is made of a signal model or a function that is adapted to the measured data or measured MR signals. In the case of fat/iron quantification in the liver, for example, such a function includes the water signal, the fat signal and a relaxation rate (for determining the iron content) as unknown parameters. Furthermore, such a function requires a number of assumptions, such as e.g. the dephasing characteristics of the fat signal or the shared effective relaxation rate for water and fat. Each assumption or each parameter that does not correspond to reality leads to distorted results in this case.
According to “Effect of echo-sampling strategy on the accuracy of out-of-phase and in-phase multiecho gradient-Echo MRI hepatic fat fraction estimation”, Y. S. Levin et al., Journal of Magnetic Resonance Imaging, volume 39 (3) 2014, pages 567-575, a small number of rapidly captured MR signals with short echo times give more accurate results during fat quantification than when more MR signals are captured with short and long echo times during a slow measurement. However a small number of rapidly captured MR signals are not the appropriate choice for determining all parameters. When determining the relaxation rate, for example, it can be advantageous also to use MR signals with long echo times.
In other words, the number of MR signals to be captured, and the way in which they are used, depends in each case on the parameter to be determined. When determining multiple parameters on the basis of the same measured MR signals, this parameter dependency of the signals to be captured represents a problem.